|
Size: 384
Comment:
|
Size: 862
Comment:
|
| Deletions are marked like this. | Additions are marked like this. |
| Line 3: | Line 3: |
| [http://www.bmj.com/cgi/content/full/314/7080/572 Bland JM, Altman DG (1997) Statistics notes: Cronbach's alpha. BMJ 314 572] | [http://www.bmj.com/cgi/content/full/314/7080/572 Bland JM, Altman DG (1997) Statistics notes: Cronbach's alpha. BMJ '''314''' 572] |
| Line 5: | Line 5: |
| The above article suggests rules of thumb for Cronbach's alpha and examples of its use. | The above article suggests rules of thumb for Cronbach's $$\alpha$$ and examples of its use. In particular a value of 0.70 is demmed to be 'satisfactory'. |
| Line 8: | Line 8: |
| $$ \frac{k}{k-1} 1 - \frac{1}{\mbox{Variance of total scores}} \mbox{Sum of item variances} $$ |
$$\frac{k}{k-1} (1 - \frac{\mbox{Sum of k item variances}}{\mbox{Variance of total scores}} )$$ In particular Bland and Altman (1997) note that ''Cronbach's alpha has a direct interpretation. The items in our test are only some of the many possible items which could be used to make the total score. If we were to choose two random samples of k of these possible items, we would have two different scores each made up of k items. The expected correlation between these scores is'' $$\alpha$$. |
A note on Cronbach's alpha
[http://www.bmj.com/cgi/content/full/314/7080/572 Bland JM, Altman DG (1997) Statistics notes: Cronbach's alpha. BMJ 314 572]
The above article suggests rules of thumb for Cronbach's $$\alpha$$ and examples of its use. In particular a value of 0.70 is demmed to be 'satisfactory'.
Cronbach's alpha is defined as
$$\frac{k}{k-1} (1 - \frac{\mbox{Sum of k item variances}}{\mbox{Variance of total scores}} )$$
In particular Bland and Altman (1997) note that
Cronbach's alpha has a direct interpretation. The items in our test are only some of the many possible items which could be used to make the total score. If we were to choose two random samples of k of these possible items, we would have two different scores each made up of k items. The expected correlation between these scores is $$\alpha$$.